The Celts in my scenario serve also as the Neutrals. In Roman times they
only lived in Gaul and Britiania but for scenario purposes I gave them
towns in Northen Hispania and Northern Africa. In Africa it was actually
the Numidians but I am only allowed 7 civs. The Hispanic region was 
actually occupied by Barbarians but they weren't as menacing as the
Germanic tribes. For the scenario the Germanic tribes build onlt Axemen
and attack you. The Celts in this region will do other stuff than just
attacking. Most of the region that the Celts occupy in Hispania was
actually owned by the Romans, but to add another challenge to the
scenario I made them a bit more difficult to conquer. Otherwise if they
only have a town or two there won't be any threat at all.